Radio broadcast .. (1922-30)

260 Radio Broadcast ITEM / 2 14 75 16 18 1 Formica panel 7 x 14 x T\ inches \ Baseboard 12 f x 7 x \ inches Poplar 2 National Velvet Vernier 4-inch Dials i General Radio Switch Lever f-inch with two Contact Points and two stops i General Radio No. 301 Knob and Pointer; for use on the tickler coil. i General Radio No. 301 Rheostat 3o-ohm. i General Radio No. 247 F Condenser .00025 mfd. logarithmic plates. 3 f-inch Lengths Formica Tubing & inch o. d. T8s inch i. d. to space Item 7 from panel i Formica Coupling Member for Item 7 (Fig. 6) i General Radio 247F Condenser .0005 mfd. logarithmic plates 35 inch Lengths Formica Tube fg inch o. d. •fs inch i. d. i Eastern Coil Corporation Coupler, Broadcast Wavelength, (15 turns on tickler, with middle tap on primary) i King Socket R730 for uv-20 1 -A Tube i Dubilier Grid Condenser .00025 mfd. Type 60 1 -G. i Daven Grid Leak .! megohm i Binding Post Panel complete with 9 binding posts i Oscillator Coupler as per Fig. 7; coupler in cludes two coils as per description later in this article. Screws, wire, spaghetti, terminal lugs, etc. Total cost of the above parts should be between $35.00 and $40.00. Fig. 7 shows the actual drilling template for the panel, but of course changes must be made if other material is used. Fig. 8 shows a coupling member for the .ooo25-mfd. variable condenser. This insulates the condenser from body capacity. Item No. 3 in the list above covers three Formica tubes which are used to set the oscillator condenser back from the panel, and to line it up with the other condenser. Item 1 1 covers spacers for the .0005 mfd. condenser. These are necessary because the design of the Velvet Vernier dial requires that the condenser be set back from the panel. The Eastern Coil Corporation coupler is known as a pickle-bottle coil, and has fewer turns than normal due to the fact that it is in circuit with the plate coil of the oscillator coupler. THE UNUSUAL OSCILLATOR COUPLER FIG. 10 shows the details of the oscillator coupler. This coupler is not the conventional type at all. In the usual coupler, the coupling between the plate and grid coils is fixed, and the coils are so large that their external fields exert an influence on all parts within a range of several inches. An attempt was made in this frequency-changer to design an oscillator which would have no effect on other parts, and this result was finally achieved. The coils shown have an exceptionally small external field, and the grid coil is placed 1 1 inches back of the oscillator variable .condenser, a position in which it has no effect on the condenser. The coils are known as "cross-wound," and have about as little distributed capacity as any coil known. The coils are wound on a f-inch core, are | inch thick, and each has 49 turns No.27Drill Drill and tap 6-32 No.27Drill COIL MOUNTING PART No.l 3/i6 Formica Stock Drill and tap COIL MOUNTING PART No.2 3^6 Formica Stock Part No.2 Coils clamped between bakelite strips Part No.l 6-32 Screws Brass Stock Solder lugs Part No.3 i COIL MOUNTING ASSEMBLY COIL MOUNTING PART No.3 FIG. 10 The details of the oscillator coupler are shown in this Figure. Small coils placed at some distance from their tuning condensers decrease the external field and the resultant coupling effects to other parts of the circuit